This invention relates to the preparation of polymers derived from 1-olefins which are characterized as having a high viscosity index, and to a process for preparing such high viscosity index oils.
Olefins can be polymerized cationically using a wide variety of catalysts. The Ziegler-Natta catalysts also have been used to polymerize olefins. The polymerized olefins obtained by prior art processes vary from low viscosity oils to high molecular weight solid polymers and copolymers. Generally, the characteristics of the polymerized olefins will depend upon and can be regulated by variations in the nature of the olefin or olefin mixture, type of catalyst or catalyst system utilized, the reaction conditions, etc. Considerable effort has been expended in recent years to develop polymers and copolymers containing 1-olefins having certain viscosity characteristics for use as synthetic lubricants and as additives for synthetic oils or mineral oils or mixtures of synthetic/mineral oils to provide modified and desirable viscosity characteristics.
In order to maximize the utility of polymerized olefins as useful additives for lubricating oil applications, it generally is preferred that the polymerized olefin be a liquid to be miscible in the lubricating oil. Accordingly, it is preferred that the polymerized olefin to be incorporated in a lubricating oil be a liquid rather than a solid. Catalyst systems have been suggested in the prior art for preparing polymers of monoolefins which are liquids. However, many of the liquids thus obtained are found to have a low viscosity index, and when added to lubricating oil compositions, the result is an undesirable lowering of the viscosity index of the lubricant.
European patent application, Publication No. 0021634 describes the preparation of synthetic lubricating oils wherein certain olefinic monomers such as ethylene, propylene and a third 1-olefin are copolymerized and thereafter dewaxed by means of a urea adduction process. The polymerization is conducted in the presence of a catalyst system comprising (a) a vanadium-containing catalyst, (b) an aluminum-containing catalyst, and (c) hydrogen. The synthetic oil prepared in this manner can be blended with other synthetic or mineral oils.
U.S. Pat. No. 3,101,327 describes a process for preparing olefin polymers having a high melt index. The increased melt index is obtained by conducting the polymerization of the olefin in the presence of certain unsaturated halogen-containing compounds. In particular, the process involves conducting the polymerization in the presence of a catalyst comprising an alky aluminum compound and a titanium halide. Optionally, a third catalyst component can be used which is an organic halide or metal halide.
U.S. Pat. No. 2,944,048 describes another catalyst composition useful in polymerizing olefins such as ethylene. The catalyst composition described in this patent comprises (1) a metal halide such as titanium halide, (2) a hydride such as aluminum hydride, and (3) an organic halide which may be an alkyl, cycloalkyl, alkenyl, aryl radical. It is indicated in this patent that the use of such a catalyst system results in polymers of higher molecular weight and high melt index.
The production of synthetic polymer oils is described in U.S. Pat. No. 3,121,061. The lubricating oils described in this patent comprise blends of two or more polypropylene fractions, one of which boils in the kerosine boiling range, and the other which boils in the "gas oil" boiling range. The polypropylene fractions are obtained from polypropylene obtained by the polymerization of propylene utilizing boron trifluoride as the catalyst and sulfuric acid as a promoter.